Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Noob needs circuit- If speaker is working blue LED is on.

Status
Not open for further replies.
Run a constant 20mA DC current through the 2 speaker wires, which lights the LED (LED will need a series resistor and a cap across it). Then just use a large cap in series with the speaker coil, to only allow the AC audio through to the speaker coil.

It should be easy enough to do and give a good safe indication of wires failing or being cut.

As far as adding the DC current injector at the amp end, that might be as easy as putting a resistor from V+ to the speaker terminal, as many 5W amps are capacitively coupled on the output to the speaker anyway.

The whole setup might only cost you a couple of resistors and caps per amp.
 
Are you saying my suggestion costs AC power?

A lot of those little amp chips (5W etc) are capacitor coupled to the speaker anyway. Adding a second cap at the speaker shouldn't affect sound power in any significant way.

The OP already said he doesn't need big amp power levels or great HiFi.
 
Are you saying my suggestion costs AC power?

A lot of those little amp chips (5W etc) are capacitor coupled to the speaker anyway. Adding a second cap at the speaker shouldn't affect sound power in any significant way.

The OP already said he doesn't need big amp power levels or great HiFi.

I'm not saying your suggestion costs AC power - I said it takes AF power.

Additionally, when connecting a second cap to the amplifier output you won't have indication of an interrupted speaker cable - which is a MUST for that application.

Consequently the circuit must be designed to monitor current flow through the speaker.
 
Last edited:
I think you misunderstood my suggestion? The LED and its filter components are placed at the end of the speaker lead (near the speaker) and DC coupled to the lead.

Then a DC current of 20mA is added at the amp end, that lights the LED at the speaker end.

Finally a large cap can be added right at the speaker itself to AC couple the speaker to the speaker lead, ie it stops the DC 20mA from going through the speaker.

None of that "takes AF power". It doesn't matter if there is any auudo content at all, and it does indicate any failure of the speaker lead, open circuit or short.
 
Insuring that you actually have a sound signal going through the speakers would require an AC signal current and voltage sense circuit, or a sound sensing microphone, so that both open and short circuit conditions are monitored. Any other detection scheme such as detecting just speaker voltage or a DC current would not insure that the speakers are actually putting out an audio signal and, I suspect, would not be acceptable in a critical government design such as an SCIF room. For such a project they almost always want a design that has the best chance of detecting all possible failure modes. Simplicity and cost are of secondary concern.
 
Good point! In that case the best system would be to use microphonic pickup on each speaker to test everything in the audio chain, including failure of the voice coil in the speaker or even the speaker cone.

I was responding to the OP (his post in #5) for a system to detect if the speaker wires were cut or unplugged.
 
Good point! In that case the best system would be to use microphonic pickup on each speaker to test everything in the audio chain, including failure of the voice coil in the speaker or even the speaker cone.

I was responding to the OP (his post in #5) for a system to detect if the speaker wires were cut or unplugged.
I missed that requirement. If that's all he needs, than one of the simpler schemes, such as monitoring a DC current in the loop as you suggested, should work.

I have a thought on that to simplify it some. If you use a high brightness LED, then you could probably get a reasonable indication with only a mA or so of current. That could likely flow through the speaker voice coil without any detrimental effects, eliminating the need for a series cap at the speaker terminals.
 
So you are suggesting putting the LED in series with the speaker coil? In that case you will need a huge bypass cap across the LED, which is basically the same as the large speaker cap in the other system.

I think either way you run it (LED in series with the wire or LED in parallel with the speaker coil), it needs a big AC cap and the LED also needs a resistor and large-ish cap.

But a couple of resistors and couple of 2200uF caps is still way within budget. :)

If the speakers are alway running at a constant white noise AC current maybe there's a way to use the LED in series with the wire to directly indicate the AC current? I'm imagining 2 diodes, 2 LEDs, 2 resistors and 3 caps...
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top